A laser diode chip is a semiconductor device, as it is known to the person skilled in the art. It generally comprises a single broad area emitting laser light. Typical dimensions are also state of the art and are 2-5 mm cavity length, preferably 4 mm. A typical width of the laser diode chip is 0.4 mm to 0.6 mm and a typical width of the emitting broad area (active area) of 50 μm to 1001 μm, preferably 90 p.m. A typical height of the emitting broad area (active area) is 1 μm to 2 μm, preferably 1.1 μm. Other sizes and dimensions of laser diode chips are possible. A laser diode chip refers to a device not packaged to any heatsink, and metalized according to the state of the art. The term single emitter laser diode is a standard term in the field.
Single emitter laser diode chips are commonly mounted flat with a relatively large surface onto a cooling surface. A laser diode chip's geometrical properties can be characterized as a relatively flat bar with two parallel large surfaces, and two sets of relatively narrow parallel surfaces, as is illustrated as element 202 in FIG. 2. In this conventional mounting, one of the large sides of the emitter laser diode chip is adjacent the cooling surface.
When high power is needed, multiple emitter laser diode chips are typically stacked together. Again, diode laser modules with multiple emitters typically mount the laser diode chips flat on the cooling surface with the relatively large surface. To stack the laser beams of each of the laser diode chips along the fast axis, most modules utilize a multi-step cooling base, where laser diode chips are mounted onto steps at different heights. In this case, each laser beam is collimated in the fast axis and slow axis separately, and turning mirrors are then used to steer all collimated laser beams to the same direction, thus causing all beams to be stacked in the fast axis. JDS Uniphase and IPG Photonics market multi-emitter modules similar to those described in this paragraph. These approaches may not be very compact.
The Trumpf bar-based diode laser product, TruDiode 3006, has eight emitters on one laser bar, and the beams are stacked along the fast axis, and then coupled into an optical fiber. A step-mirror assembly is used in to rotate the beams 90 degrees and achieve the stacking. This approach suffers from similar drawbacks already discussed.
LIMO Lissotschenko Mikrooptik GmbH of Dortmund, Germany makes a tilted lens array product, called BTS, that achieves similar goals. The BTS product however also has the drawbacks previously discussed.
Various attempts to vertically stack laser emitter chips have been made. These are discussed in the following paragraphs.
U.S. Pat. No. 7,801,190 to Jenoptik discloses, in one embodiment, a laser diode stack, which is sandwiched between two coolers and attached to these coolers employing a solder layer, which is discontinuous so that it doesn't short the laser diodes. Each laser diode chip in the stack is sandwiched between two sub-mounts of different thickness and placed in a symmetrical position relative to top and bottom edges of the sub-mounts. At least one disadvantage of the structure disclosed in U.S. Pat. No. 7,801,190 is the need to have symmetric cooling carriers on both sides of the laser diode. Another disadvantage is the relatively long heat dissipation path from laser emitter to cooling carrier.
U.S. Pat. No. 7,515,346 to Coherent discloses vertically stacked laser diodes. Each laser diode chip is soldered to an electrically insulation sub-mount, preferably of diamond, and bonded to a surface of a common heat sink. The sub-mounts are partially metallized to allow connecting the laser diodes chips in series via strip electrodes. At least one disadvantage of the laser diode chip assembly in U.S. Pat. No. 7,515,346 is the complexity of the cooling carrier design.
U.S. Pat. No. 8,611,389 to Shinko Electric shows the assemblage of a package component comprising a laser diode. Several package components may be attached to a heat block to form vertically stacked laser diodes. The laser diodes are connected to each other via solder layers and the wiring layers on the front and back side of each laser diode are shorted via a through hole in one of the walls forming package component. At least one disadvantage of the laser diode assembly in U.S. Pat. No. 8,611,389 is the complexity of the packaging process and the long heat dissipation path.
European Patent Application EP2477285A1 describes a multitude of laser diodes each comprising an arbitrary number of emitting apertures that are embedded in a medium with good thermal conductivity, such that all laser diodes are preferably oriented perpendicular to a common mounting surface and emit parallel to each other and preferably in the plane of the mounting surface. Thus a stack of laser diodes results with the laser diodes being oriented perpendicular to the mounting surface emitting parallel to the mounting surface. At least one disadvantage of this laser diode assembly is the electrical insulation and the electrical contacting of the individual laser diodes while ensuring good cooling and low stress in the laser diode. Furthermore the application claims this set-up to be used for spatial or spectral beam combining to enhance brightness, but does not describe or claim any method to align the emitting apertures to each other, which is an essential feature for high brightness diode laser systems
As a result, new and improved apparatus and methods to achieve a vertical assembly of laser emitter diodes also called laser diode chips are needed.